Examples of a cutting insert (hereinafter also simply referred to as “insert”) used for cut processing a work material, such as a metal, include a cutting insert disclosed in Japanese Unexamined Patent Application Publication No. 2004-195563A (Patent Document 1) and WO/2010/114094 (Patent Document 2). The insert disclosed in Patent Document 1 has first cutting edges whose height becomes gradually lower toward corner portions. The first cutting edge has a linear shape when viewed from a side. The insert disclosed in Patent Document 2 has first corner cutting edges that function as first sub cutting edges, second corner cutting edges, and main cutting edges located between these corner cutting edges. The first corner cutting edge functions as a bottom cutting edge. When attached to an end mill main body (holder), the second corner cutting edge is located on an outer periphery side of the end mill main body and functions as an auxiliary cutting edge.
With the insert disclosed in Patent Document 1, since the first cutting edge has the linear shape when viewed from a side, when the first cutting edge bites into the work material, sometimes the whole of the first cutting edge simultaneously comes into contact with the work material. In this case, a problem arises in which chatter vibration easily occurs because a load exerted on the first cutting edge changes rapidly.
With the insert disclosed in Patent Document 2, the main cutting edge is formed such that the height thereof increases more as the main cutting edge becomes separated from the first corner cutting edge. Thus, chips cut by the main cutting edge flow so as to become trapped inside the holder. Even in this case, in surface milling and shoulder machining, the chips can be favorably discharged outside. However, in the case of groove machining, a discharge direction of the chips is limited to the opposite side to a travel direction (feed direction) of a cutting tool. Thus, the chips that flowed so as to be trapped inside the holder cannot be favorably discharged, and if the main cutting edge makes contact once more with the work material in the state in which the chips are trapped, the chips may become caught between the main cutting edge and the machined surface of the work material.
In light of the foregoing, it is an object of an aspect of the present invention to provide a cutting insert capable of performing stable cut processing and also capable of discharging chips in a stable manner.